Rotating anode x-ray tube



United States Patent 2,926,270 ROTATING AN ODE X-RAY TUBE Michael]. Zunick, west Allis, Wis., assignor to General Electric Company, a corporation of New York- Application December so, 1951, Serial No. 705,883

2 (Ilaims. ((11.313-60) This invention relates to improvements in rotating anode type X-ray tubes.

Major objects are as follows:

(a) Substantially to increase unit area loading.

(b) To permit employment of a small focal spot (for example, a 0.3 mm. spot) with load ratingsjn excess of those obtainedheretofore in tubes employing a rotating anode of comparable size;

To avoid the necessity of employing large rotary targets, such as 8"and 9" targets to-gain the load ratings heretofore not possible with smaller targets.

Increased need for high unit area loading of rotary anode type X-ray tubes, particularly those employed for medical diagnostic or industrial application has resulted in a progressive increase 'in target diameter? Serious limitations have'been encountered, however, from both an engineering and a manufacturing standpoint in respect to the design and production of ,dense tungsten target tubes in the range of 8" to .10" in diameter or larger. Formed dish anodes of this size are extremely difiicult to produce, and the resulting increase in overall tubeenvelope dimensions is undesirable in many instances;' The optimum goal has, therefore, been the solution of the problem of obtaining increased unit area loading without substantially increasing anode diameters. Prior to the concept of the present invention that objective had not successfully been achieved.

Applicants broad concept, as stated above, teaches the incorporation in an otherwise conventionally designed rotary anode X-ray tube, of means preferably comprising a wobble mechanism for oscillating an armature type rotating target with respect to a predetermined point along its axis and in one or more of the planes thereof effectively to increase the amount of fresh metal presented to the electron beam per target revolution. This is accomplished by altering the path defined by beam impingrnent from a circular configuration to a wavy or generally sinusoidal path extending through a circular orbit. To accomplish this objective in a manner that the spot shows no movement, the geometry of the target surface must conform to an arc of a circle transcribed by a radius rotated about the wobble point of the anode armature structure.

In the drawings, illustrating a rotating anode X-ra tube incorporating the inventive concept:

Figure 1 illustrates the contour of the rotary anode target for elimination of spot movements as the target is oscillated about its wobble point.

Figure 2 illustrates a preferred embodiment of the invention wherein a target-carrying armature is mounted within an X-ray tube in a manner to allow the target to be pivoted about a predetermined point along its axis of rotation by external means while maintaining the tube interior sealed from the atmosphere.

Figure 3 is a sectional view along line 3-3 of Fig. 2.

Fig. l is illustrative of the geometry of target face configuration. A known type of rotating anode tube 10 includes a glass envelope 11, a cathode assembly 12 known in the art.

See

supported. from an inverted end portion of envelope 11' and a rotary target 14 driven by an armature 15 disposed within an elongate envelope neck portion 16, armature 15 being suitablyjournalled by means not shown to be rotated by an external field structure in a manner well Target 14 is suitably connected to a cathode terminal 18 to complete the structure.

Assuming tube 10 connected in known X-ray apparatus in operation, a beam of high energy electrons flows from cathode 12 to strike rotating target 14 to generate X-rays which pass through a window portion 22, preferably of reduced thickness, provided in envelope 11. As target 14 rotates, fresh metal is fed to beam 20 during each revolution, but the amount of metal so fed is limited to the single circular configuration defined by the beam. If, however, means are provided simultaneously to oscillate the target about an axis passing through point 23 the target path so defined is substantially lengthened, hence a'greateramoun-t of metal is .fed to the beam per revolution, with a consequent increase in unit area loading.

Fig. 2 illustrates structure for practicing the improved method of increasing unit area loading. Tube 110, which may otherwise be identical to tube 10 of Fig. 1 is provided with an anode neck portion 116 of sufiicient length to house armature 115 in substantially the position of armature 15 of Fig. l, but flexibly mounted to tube envelope 116' to allow some pivoting in respect to a point in its axis of rotation corresponding to point 23 of Fig. 1. Drew the small focal spot of beam, for example, a 0.3 mm. spot, target 14 may be 'pivoted through only a small arcv to obtain the desired end result.

, tubular member 28 extending .aft in spaced concentric relation to innerwalI 26 to project outwardly of the envelope as shown. The inner end so of member 28" has bonded thereto an axially disposed bellows 32, preferably but not necessarily being ofmetal. The opposite end of bellows 32 is bonded to member 34. The bellows being readily deformable to permit rod 43 and armature support member 34 to be pivoted about a point in the axis thereof determined by the radius of a circle an arc of which determines the curvature of guide member 46,

later described. The pivot point thus determined corresponds to center point 23 of circle 50, Fig. 1.

Journal member 34 includes a shank portion 35 leading to an enlarged cylindrical housing portion 36 and defining, intermediate those portions, an annular shoulder 38 to which the forward end of bellows 32 is bonded in fluid sealing engagement therewith. Bearings 37, 38 are suitably disposed within the cylinder housing 36 to provide journally support for shaft 40 of a conventional rotating anode type armature 42 for the rotation of target 14. The aft end of shank portion 35 of member 34 has threadedthereto at 42 the actuating rod 43 extendingin axial spaced relation through tube 28 to terminate in a portion 45, of reduced diameter, to which is mounted the above-mentioned arcuate guide member 46, held thereto in clamped engagement by nut 47.

Target 14 has its beam receiving faces contoured in registrywith an arc of circle 56, Fig. 1, hence pivoting of target 14 in respect to a point corresponding to point 23 may be accomplished without varying either the spacing between cathode and target while presenting fresh metal to the beam without change of the target contour presented thereto. Underthese conditions the spot is said to show no movement, a condition which is mandatory in commercially acceptable X-ray equipment.

Returning to Fig. 2, the structure above described is so designed that the outer end of rod 43 may be reciprocated in a vertical plane, as shown, to effect the desired pivoting of target 14. It will be noted that bellows 32 serves as part of the inner neck wall in a manner to permit flexing of the anode structure internally of the tube while maintaining the envelope sealed to the atmosphere.

As is apparent, the outer end of rod 43 could be pivoted in any plane by employment of a spherical guide member 46 and a complementary guide channel, but as shown, it is constrained to pivot in a single plane. To prevent the spot from showing movement in the structure illustrated, the target is constrained to pivot only in a plane in line with the long dimension of the cathode element as shown in Fig. 1. Guide member 46, hence rod 43, is accordingly constrained for movement in the single desired plane by channel defining members 52 and 53, Fig. 2, attached to apertured support bracket 55- by screws 56. The outer end of tube 28, threadedly engages bracket 55 and is locked thereto by nut 57. Outer face 60 of bracket 55 is arced to complement the inner face of guide member 46, and the outer face of member 46, of like curvature, complementarily engages the wall surfaces of channel members 52 and 53 to securely position member 46 while permitting movement of that member within the arc defined by the channel forming mem bers. Actuating means, such as solenoid 61 for the vertical reciprocation of rod 43 may be connected through linkage 63. Conventional externally disposed armature rotating field coils 64 are shown to complete the assembly.

While the structure of Fig. 2, shown for exemplary purposes, limits target movement to a single plane, the invention is not so limited, and it may be found advan tageous to utilize for certain purposes, the universal character of the pivoting principle shown to move the target in respect to a plurality of axes.

What I claim is:

1. In an X-ray tube of the rotating anode type including an evacuated envelope and a target having a curved face mounted forrotation therein in the path of an electron beam, an elongate member on which said target is 'journalled for rotation and which extends exteriorly of the envelope, means flexibly and sealingly joining said elongate member with said envelope, and a universal guide means rigidly connected with said elongate member, said guide means including a curved surface that is restrained to translate only along a circle that also defines said curved target face, and oscillating means connected with said elongate member for rocking the same about a fixed point lying on the axis of anode rotation at the center of the circle and thereby moving said 1 target face in the path of said circle through an are having equal length of the arc through which said curved surface moves during oscillation.

2. In an X-ray tube including an evacuated envelope, a cathode, an anode, and means mounting said anode for rotation in spaced relation to said cathode, said means including an armature and a journal member for rotational support of the armature, said envelope including an elongated neck with a reentrant portion forming a concentric inner wall, a rigid concentric extension bonded to said inner wall, a bellows interposed between and bonded at opposite ends to said extension and said journal member to maintain the tube interior sealed from the atmosphere, means disposed externally of said envelope for the pivotal support of said journal member,

7 said pivotal support means comprising an elongate member extending from said journal member to the exterior of the tube and adapted for rotation of the armature with respect thereto and for oscillation with respect to the envelope about a point on the axis of anode rotation, and means operable from the exterior of the envelope to eliect pivoting of said journal member about said point through the agency of said elongate member.

References Cited in the file of this patent UNITED STATES PATENTS 

